1. Field of the Invention
This invention relates generally to a system and method for providing an overlay torque command to control an electric power steering (EPS) motor and, more particularly, to a system and method for providing an overlay torque command to control an EPS motor, where the method employs a six-dimensional vehicle motion model including a one-track linear bicycle model and a one-degree of freedom steering column model for modeling vehicle steering to determine a steering control goal and provide model predictive control (MPC) that determines an optimal total steering column torque from which the overlay torque command is determined.
2. Discussion of the Related Art
Advances in sensor and actuator technologies have enabled the development of driver assistance systems (DAS) to prevent road accidents, especially those caused by driver's mistakes or inattention. Several types of DAS, such as anti-lock braking system (ABS), electronic stability control (ESC), adaptive cruise control (ACC), lane departure warning (LDW) system, lane change assist (LCA), forward collision alert (FCA), and lane keeping assist (LKA), are already in production vehicles. Active safety technology is currently becoming a major area of research in the automotive industry. Collision imminent braking is an effective way of avoiding or mitigating collision by applying brakes. On the other hand, collision avoidance steering may allow collision avoidance in some situations when braking alone can only mitigate it.
Collision avoidance systems are known in the art for providing automatic steering of a subject vehicle to avoid a slower or stopped object in front of the subject vehicle in the event that the vehicle driver does not take evasive action on his own. Known collision avoidance systems provide warnings to the vehicle driver and depending on whether the driver takes evasive action, may provide automatic braking and/or automatic steering. If the system determines that automatic steering is necessary to avoid a collision, the system must calculate a safe steering path for the subject vehicle to provide the steering control. Some of those systems are able to detect lane markings so as to calculate the steering path of the subject vehicle to make a lane change for collision avoidance purposes. Those collision avoidance systems also provide steering commands that cause the subject vehicle to follow the calculated steering path to provide the vehicle steering.
The object detection sensors for these types of systems may use any of a number of technologies, such as short range radar, long range radar, cameras with image processing, laser or LiDAR, ultrasound, etc. The object detection sensors detect vehicles and other objects in the path of a subject vehicle, and the application software uses the object detection information to provide warnings or take actions as appropriate. The warning can be a visual indication on the vehicles instrument panel or in a head-up display (HUD), and/or can be an audio warning or other haptic feedback device, such as seat shaking. In many vehicles, the object detection sensors are integrated directly into the front bumper or other fascia of the vehicle.
U.S. Pat. No. 8,190,330, titled, Model Based Predictive Control for Automated Lane Centering/Changing Control Systems, issued May 29, 2012, assigned to the assignee of this application and herein incorporated by reference, discloses a system and method for providing steering control for lane changing or lane centering purposes in an autonomous or semi-autonomous vehicle driven system. U.S. Pat. No. 8,527,172, titled, Vehicle Collision Avoidance and Warning System, issued Sep. 3, 2013, assigned to the assignee of this application and herein incorporated by reference, discloses a collision avoidance system that employs combined automated braking and steering.
U.S. Patent Application Publication No. 2013/0218396 to Moshchuk et al., assigned to the assignee of this application and herein incorporated by reference, discloses a system and method for providing enhanced vehicle control including providing automatic steering assistance. The '396 application describes a collision avoidance system that employs a steering model using a four-dimensional one-track linear bicycle model to model the vehicle dynamics. The four-dimensional model is used to generate a road wheel angle command necessary to control an electric power steering (EPS) system to provide the steering assistance, where the road wheel angle command is converted to a torque command that is applied to the electric motor in the EPS system. The '396 application uses proportional-integral-derivative (PID) control to convert the road wheel angle command to a torque command for the EPS system. However, employing PID control for this purpose requires extensive tuning to achieve good performance and robust operation at all vehicle speeds. Tuning of the PID control is time consuming and the steering control resulting therefrom may become unstable during tuning. Further, compensation for a steering actuator delay is required.